"It is difficult to get a man to understand something, when his salary depends upon his not understanding it!" This generalizes. Good luck funding research into a question to which people really don't want an answer to. There's some valid reasons to not want an answer - eugenics was and is a real thing, and its terrifying. For a while we seemed to skate by on a kind of "gentleman's agreement" to not look into it too much. Just like there was a kind of "gentleman's agreement" to not point out the facts of sexual dimorphism in humans, as a paean to feminism. When feminists start claiming superiority of females to males, or extremist egalitarians start claiming we're all the same, I think an argument could be made that they have invalidated the agreement. Unfortunately.